ER & Golgi

Question 1

what mediates folding of proteins

Answer 1

chaperone proteins

Question 2

what mediates disulphide bridge formation in proteins

Answer 2

protein disulphide isomerase (PDI)

Question 3

what is oligomerisation

Answer 3

the assembly of multi-protein complexes

Question 4

what 3 things are required for ribosome docking

Answer 4

signal peptide/signal sequence (SP), signal recognition particle (SRP), SRP receptor

Question 5

how do proteins enter the ER lumen

Answer 5

through the translocation channel (translocon)

Question 6

what occurs during translocation in type 1 proteins

Answer 6

signal sequence is cleaved at the n terminus by signal peptidase

Question 7

what is the defining property of stop/start transfer sequences

Answer 7

they are hydrophobic so will be found in the ER membrane

Question 8

how is a hydropathy plot read

Answer 8

the hydrophobic areas represent the hydrophobic domains of signal sequences

Question 9

what is an internal signal sequence

Answer 9

internal signal sequences exist in the middle of the polypeptide chain rather than the end, so are not cleaved

Question 10

4 features of a type 1 transmembrane protein

Answer 10

single pass
cleaved signal sequence
stop sequence in the ER membrane
C terminus in cytosol

Question 11

key difference between type 2 & type 3 TM proteins

Answer 11

orientation, N terminus in cytosol for type 2 protein, C terminus in cytosol for type 3 protein

Question 12

what determines the orientation of the protein

Answer 12

whether positive amino acid side chains are
in front of or behind the signal sequence. If they are in front of the Signal Sequence then N terminus in cytosol
If behind the signal sequence then C terminus in cytosol

Question 13

what are type 4 TM proteins

Answer 13

they have 2 or more transmembrane domains (stop/start sequences)

Question 14

what are the 2 sides of the Golgi and where do they face

Answer 14

cis side faces nucleus

trans side faces nearest plasma membrane

Question 15

what is the sequence for forward Golgi traffic

Answer 15

er to cis Golgi network to cis cisterna to medial cisterna to trans cisterna to plasma membrane

Question 16

what is the cisternal progression model

Answer 16

enzymes move sequentially backwards from trans to cis stacks through retrograde vesicle transport, substrates stay in the same compartments

Question 17

what happens during clatherin mediated endocytosis of LDL

Answer 17

LDL binds to receptor which migrates to clatherin pit
Clathrin coated vesicle is uncoated once inside the cell
`Vesicle binds with endosome of ph5 and receptor releases LDL
Late endosome binds with lysosome and cholesterol, amino acids and small peptides form
Cholesterol is released into cytosol for new membrane formation

Question 18

how does dynamin work

Answer 18

it polymerises around the vesicle bud neck and hydrolyses GTP to cause a conformational change, this stretches the neck until the bud pinches off

Question 19

what is the difference between COP1 and COP2

Answer 19

COP1 is the protein coat involved in retrograde enzyme transport, COP2 is the protein coat involved in movement from ER to Golgi. They drive transport in opposite directions

Question 20

what is the function of SNARES

Answer 20

they are involved in the membrane fusing process, v-snare binds to t-snare to form a tight hydrophobic complex